# Copyright 2019 The TensorFlow Authors. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# ==============================================================================
"""ROI-related ops."""

from __future__ import absolute_import
from __future__ import division
from __future__ import print_function

import tensorflow as tf

from official.vision.detection.ops import nms
from official.vision.detection.utils import box_utils


def multilevel_propose_rois(rpn_boxes,
                            rpn_scores,
                            anchor_boxes,
                            image_shape,
                            rpn_pre_nms_top_k=2000,
                            rpn_post_nms_top_k=1000,
                            rpn_nms_threshold=0.7,
                            rpn_score_threshold=0.0,
                            rpn_min_size_threshold=0.0,
                            decode_boxes=True,
                            clip_boxes=True,
                            use_batched_nms=False,
                            apply_sigmoid_to_score=True):
  """Proposes RoIs given a group of candidates from different FPN levels.

  The following describes the steps:
    1. For each individual level:
      a. Apply sigmoid transform if specified.
      b. Decode boxes if specified.
      c. Clip boxes if specified.
      d. Filter small boxes and those fall outside image if specified.
      e. Apply pre-NMS filtering including pre-NMS top k and score thresholding.
      f. Apply NMS.
    2. Aggregate post-NMS boxes from each level.
    3. Apply an overall top k to generate the final selected RoIs.

  Args:
    rpn_boxes: a dict with keys representing FPN levels and values representing
      box tenors of shape [batch_size, feature_h, feature_w, num_anchors * 4].
    rpn_scores: a dict with keys representing FPN levels and values representing
      logit tensors of shape [batch_size, feature_h, feature_w, num_anchors].
    anchor_boxes: a dict with keys representing FPN levels and values
      representing anchor box tensors of shape [batch_size, feature_h,
      feature_w, num_anchors * 4].
    image_shape: a tensor of shape [batch_size, 2] where the last dimension are
      [height, width] of the scaled image.
    rpn_pre_nms_top_k: an integer of top scoring RPN proposals *per level* to
      keep before applying NMS. Default: 2000.
    rpn_post_nms_top_k: an integer of top scoring RPN proposals *in total* to
      keep after applying NMS. Default: 1000.
    rpn_nms_threshold: a float between 0 and 1 representing the IoU threshold
      used for NMS. If 0.0, no NMS is applied. Default: 0.7.
    rpn_score_threshold: a float between 0 and 1 representing the minimal box
      score to keep before applying NMS. This is often used as a pre-filtering
      step for better performance. If 0, no filtering is applied. Default: 0.
    rpn_min_size_threshold: a float representing the minimal box size in each
      side (w.r.t. the scaled image) to keep before applying NMS. This is often
      used as a pre-filtering step for better performance. If 0, no filtering is
      applied. Default: 0.
    decode_boxes: a boolean indicating whether `rpn_boxes` needs to be decoded
      using `anchor_boxes`. If False, use `rpn_boxes` directly and ignore
      `anchor_boxes`. Default: True.
    clip_boxes: a boolean indicating whether boxes are first clipped to the
      scaled image size before appliying NMS. If False, no clipping is applied
      and `image_shape` is ignored. Default: True.
    use_batched_nms: a boolean indicating whether NMS is applied in batch using
      `tf.image.combined_non_max_suppression`. Currently only available in
      CPU/GPU. Default: False.
    apply_sigmoid_to_score: a boolean indicating whether apply sigmoid to
      `rpn_scores` before applying NMS. Default: True.

  Returns:
    selected_rois: a tensor of shape [batch_size, rpn_post_nms_top_k, 4],
      representing the box coordinates of the selected proposals w.r.t. the
      scaled image.
    selected_roi_scores: a tensor of shape [batch_size, rpn_post_nms_top_k, 1],
      representing the scores of the selected proposals.
  """
  with tf.name_scope('multilevel_propose_rois'):
    rois = []
    roi_scores = []
    image_shape = tf.expand_dims(image_shape, axis=1)
    for level in sorted(rpn_scores.keys()):
      with tf.name_scope('level_%d' % level):
        _, feature_h, feature_w, num_anchors_per_location = (
            rpn_scores[level].get_shape().as_list())

        num_boxes = feature_h * feature_w * num_anchors_per_location
        this_level_scores = tf.reshape(rpn_scores[level], [-1, num_boxes])
        this_level_boxes = tf.reshape(rpn_boxes[level], [-1, num_boxes, 4])
        this_level_anchors = tf.cast(
            tf.reshape(anchor_boxes[level], [-1, num_boxes, 4]),
            dtype=this_level_scores.dtype)

        if apply_sigmoid_to_score:
          this_level_scores = tf.sigmoid(this_level_scores)

        if decode_boxes:
          this_level_boxes = box_utils.decode_boxes(this_level_boxes,
                                                    this_level_anchors)
        if clip_boxes:
          this_level_boxes = box_utils.clip_boxes(this_level_boxes, image_shape)

        if rpn_min_size_threshold > 0.0:
          this_level_boxes, this_level_scores = box_utils.filter_boxes(
              this_level_boxes, this_level_scores, image_shape,
              rpn_min_size_threshold)

        this_level_pre_nms_top_k = min(num_boxes, rpn_pre_nms_top_k)
        this_level_post_nms_top_k = min(num_boxes, rpn_post_nms_top_k)
        if rpn_nms_threshold > 0.0:
          if use_batched_nms:
            this_level_rois, this_level_roi_scores, _, _ = (
                tf.image.combined_non_max_suppression(
                    tf.expand_dims(this_level_boxes, axis=2),
                    tf.expand_dims(this_level_scores, axis=-1),
                    max_output_size_per_class=this_level_pre_nms_top_k,
                    max_total_size=this_level_post_nms_top_k,
                    iou_threshold=rpn_nms_threshold,
                    score_threshold=rpn_score_threshold,
                    pad_per_class=False,
                    clip_boxes=False))
          else:
            if rpn_score_threshold > 0.0:
              this_level_boxes, this_level_scores = (
                  box_utils.filter_boxes_by_scores(this_level_boxes,
                                                   this_level_scores,
                                                   rpn_score_threshold))
            this_level_boxes, this_level_scores = box_utils.top_k_boxes(
                this_level_boxes, this_level_scores, k=this_level_pre_nms_top_k)
            this_level_roi_scores, this_level_rois = (
                nms.sorted_non_max_suppression_padded(
                    this_level_scores,
                    this_level_boxes,
                    max_output_size=this_level_post_nms_top_k,
                    iou_threshold=rpn_nms_threshold))
        else:
          this_level_rois, this_level_roi_scores = box_utils.top_k_boxes(
              this_level_rois, this_level_scores, k=this_level_post_nms_top_k)

        rois.append(this_level_rois)
        roi_scores.append(this_level_roi_scores)

    all_rois = tf.concat(rois, axis=1)
    all_roi_scores = tf.concat(roi_scores, axis=1)

    with tf.name_scope('top_k_rois'):
      _, num_valid_rois = all_roi_scores.get_shape().as_list()
      overall_top_k = min(num_valid_rois, rpn_post_nms_top_k)

      selected_rois, selected_roi_scores = box_utils.top_k_boxes(
          all_rois, all_roi_scores, k=overall_top_k)

    return selected_rois, selected_roi_scores


class ROIGenerator(object):
  """Proposes RoIs for the second stage processing."""

  def __init__(self, params):
    self._rpn_pre_nms_top_k = params.rpn_pre_nms_top_k
    self._rpn_post_nms_top_k = params.rpn_post_nms_top_k
    self._rpn_nms_threshold = params.rpn_nms_threshold
    self._rpn_score_threshold = params.rpn_score_threshold
    self._rpn_min_size_threshold = params.rpn_min_size_threshold
    self._test_rpn_pre_nms_top_k = params.test_rpn_pre_nms_top_k
    self._test_rpn_post_nms_top_k = params.test_rpn_post_nms_top_k
    self._test_rpn_nms_threshold = params.test_rpn_nms_threshold
    self._test_rpn_score_threshold = params.test_rpn_score_threshold
    self._test_rpn_min_size_threshold = params.test_rpn_min_size_threshold
    self._use_batched_nms = params.use_batched_nms

  def __call__(self, boxes, scores, anchor_boxes, image_shape, is_training):
    """Generates RoI proposals.

    Args:
      boxes: a dict with keys representing FPN levels and values representing
        box tenors of shape [batch_size, feature_h, feature_w, num_anchors * 4].
      scores: a dict with keys representing FPN levels and values representing
        logit tensors of shape [batch_size, feature_h, feature_w, num_anchors].
      anchor_boxes: a dict with keys representing FPN levels and values
        representing anchor box tensors of shape [batch_size, feature_h,
        feature_w, num_anchors * 4].
      image_shape: a tensor of shape [batch_size, 2] where the last dimension
        are [height, width] of the scaled image.
      is_training: a bool indicating whether it is in training or inference
        mode.

    Returns:
      proposed_rois: a tensor of shape [batch_size, rpn_post_nms_top_k, 4],
        representing the box coordinates of the proposed RoIs w.r.t. the
        scaled image.
      proposed_roi_scores: a tensor of shape
        [batch_size, rpn_post_nms_top_k, 1], representing the scores of the
        proposed RoIs.

    """
    proposed_rois, proposed_roi_scores = multilevel_propose_rois(
        boxes,
        scores,
        anchor_boxes,
        image_shape,
        rpn_pre_nms_top_k=(self._rpn_pre_nms_top_k
                           if is_training else self._test_rpn_pre_nms_top_k),
        rpn_post_nms_top_k=(self._rpn_post_nms_top_k
                            if is_training else self._test_rpn_post_nms_top_k),
        rpn_nms_threshold=(self._rpn_nms_threshold
                           if is_training else self._test_rpn_nms_threshold),
        rpn_score_threshold=(self._rpn_score_threshold if is_training else
                             self._test_rpn_score_threshold),
        rpn_min_size_threshold=(self._rpn_min_size_threshold if is_training else
                                self._test_rpn_min_size_threshold),
        decode_boxes=True,
        clip_boxes=True,
        use_batched_nms=self._use_batched_nms,
        apply_sigmoid_to_score=True)
    return proposed_rois, proposed_roi_scores
